This invention relates to a method of and means for scrambling an input analog signal that is to be transmitted through a communication channel such that the transmitted signal is unintelligible, but can be descrambled after transmission to recover the original input signal.
Many techniques are available for scrambling analog signals, particularly audio signals such as speech. Such techiques usually involve a scrambling operation at frequencies much higher than audio frequencies; and, as a consequence, the equipment, usually involving high frequency modulation, demodulation and transmission, becomes complicated and expensive. Often, the bandwidth of the transmission must be considerably wider than the bandwidth of the original signal. A great deal of interest has been expressed in having scramblers that operate in an acoustic medium and over telephone lines where the frequencies used for communication cation are limited to the audio frequencies.
It is therefore an object of the present invention to provide a new and improved technique for scrambling and descrambling audio signals at audio frequencies thereby expanding due to communication channels utilizing only audio frequencies without requiring modulation or demodulation.